History of the Unit: A 9-month Regiment formed of Companies recruited in Blair and Huntingdon counties.

In the Antietam Campaign: Antietam was their first combat engagement, the Regiment having been in service just over a month by that time. They were in the lead of Mansfields XII Corps attack across the Cornfield, reaching into the West Woods at the Dunkard Church before being driven back with high casualties. Lt Theodore Flood of Company C later recalled:

"... and then marched to South Mountain , reaching there on Sunday evening, just as the battle of South Mountain was finished.""... we marched to the battlefield of Antietam, where we went into that awful conflict early on the morning of Wednesday, the seventeenth day of September. While waiting in line of battle for orders to advance and fire, Adjutant Johnston, of our regiment, was mortally wounded and died in a few hours. The battle was on in full force. Confederate pickets were shooting down our officers, shells were flying over our heads, horses and men lay dead on the field. We were ordered forward in line of battle, and Captain Wallace stepped out in front of the company, waving his sword, and called out, 'Boys, remember our battle-cry, In God We Trust.' This was taken up as a battle-cry by adjoining companies along the line, until we reached the edge of a woods, where we were halted and ordered to fire. The enemy met us with a heavy charge. We could see them coming in line of battle as we loaded and fired. General Mansfield fell mortally wounded just in the right front of our regiment while reconnoitering . The blood from his wound reddened his long white beard. As we stood firing into the ranks of the enemy the second man to me, George A. Simpson, while bravely holding the flag aloft, was hit with a bullet from a Confederate gun, which pierced his brain, and he fell dead. A second man picked up the flag, and he was shot clown. A third, and he fell; the fourth took it up, and he was shot and fell. Then Sergeant W.W. Greenland picked up tile flag, stained with the blood of Simpson, and Captain Wallace, taking it in charge, carried it across the field to the rear of the nearest battery, and there he, aided by Captains Bell and McKeage and Lieutenant Thomas McCamant, rallied about two hundred of the regiment, who remained in support, while our batteries operated with deadly execution upon the enemy, during the rest of tile conflict. The conflict was raging all along the line of tile army; the Confederates were pressing us hard; our line was broken, and a new line of battle was formed in the rear. Two hundred and twenty-nine men of our regiment were killed and wounded in about twenty minutes; of these 84 were slightly wounded, but not disabled, and therefore were not reported. It was a dreadful struggle and we were thrust into the very furnace of battle."
(from Wallace)

The remainder of the War: They marched to Fredericksburg (Va) in December 1862, and were on Burnside's "Mud March" of late January 1863, but were not in combat again until Chancellorsville in May. The Regiment was mustered out following that battle, at the end of its term of service.

References, Sources, and other Notes: Source: Wallace, William W., ed., History of the One Hundred and Twenty-fifth Regiment Pennsylvania Volunteers, Philadelphia: J.B. Lippincott Company, 1906, excerpted online in the history of the Huntingdon (Pa) Presbyterian Church; and
Bates, Samuel P., History of the Pennsylvania Volunteers, 1861-65, Harrisburg: 1868-1871, extracted online at Pennsylvania in the Civil War.